Re: [ADSM-L] measuring shoeshining ?

2007-04-17 18:54:40
Subject: Re: [ADSM-L] measuring shoeshining ?
From: Peter Billam <peter.billam AT DPIW.TAS.GOV DOT AU>
Date: Wed, 18 Apr 2007 08:53:57 +1000
Greetings.  I wrote:
>Is there a good way of collecting daily shoeshining statistics ?

Roger Deschner wrote:
> Interesting question. I would simply measure tape throughput.
> ... You could scan the activity log for migration and reclamation
> completed stats, and also look for backup sessions that mounted a
> tape and grab their accounting stats.

Is there a good SQL query for throughput ?  Throughput grouped by
node is what's needed for the direct-to-disc case.

> ..., you can open a door on the back and have access to the back
> of the tape drives. I should borrow a doctor's stethescope and see
> if I can hear anything from the back.

In our server-room you wouldn't hear much, now that our fierce new
air contitioners have been installed :-)

> I wonder if the tape drives many of us use (LTO and SDLT) collect any
> of this information. ...
> Is anybody from someplace like Quantum or the LTO consortium listening?

The hardware could collect filemark counts.  (Or, after the fact,it
might be easy to read the tape and count filemarks ?) (Is filemark
the right word ?) But I don't see how it could know whether the
filemark was an emergency motivated by buffer-underrun.
Maybe only the application (dsmserv) knows that ?

And maybe that's the disconnect here; maybe only the driver and drive
know whether a mark-and-backspace was done, and the application knows
if it's expecting more data in the same stream, and maybe they don't
talk to each other ?

If the information _is_ to be had in one place, it's probably the scsi
tape driver, like drivers/scsi/st.c and Documentation/scsi/st.txt,
because that wrestles with the buffers, filemarks, backspacing etc.

I'd want a figure in shoeshines/Gb, or Gb/shoeshine.
One shoeshine is probably something like a mark-and-backspace
caused by slow supply of an ongoing data stream.

I can't help feeling it's an important statistic. I know I'd love to
have it to have it, to properly motivate purchasing decisions...

Regards, Peter

AUS/TAS/DPIW/CIT/Servers hbt/lnd/l8   6233 3061
Pasari, pasarimos    dice el agua    y canta la verdad contra la piedra
 -- Pablo Neruda

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